Susceptor structure

ABSTRACT

A microwave energy interactive structure includes a first susceptor film including a first layer of microwave energy interactive material supported on a first polymer film, a moisture-containing layer joined to the first layer of microwave energy interactive material, an adjoining layer joined to the moisture-containing layer such that the moisture-containing layer is disposed between the susceptor film and the adjoining layer, and a second layer of microwave energy interactive material on a side of the adjoining layer opposite the moisture-containing layer. The adjoining layer may be joined to the moisture-containing layer by a discontinuous adhesive layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is continuation-in-part of International ApplicationNo. PCT/US2009/063963, filed Nov. 11, 2009, which claims the benefitunder 35 U.S.C. §119(e) of U.S. Provisional Application No. 61/198,981,filed Nov. 12, 2008, both of which are incorporated by reference hereinin their entirety.

BACKGROUND

Susceptors have been used in conventional microwave heating packages toenhance the heating, browning, and/or crisping of food items. Asusceptor generally comprises a thin layer of microwave energyinteractive material (generally less than about 100 angstroms inthickness, for example, from about 60 to about 100 angstroms inthickness, and having an optical density of from about 0.15 to about0.35, for example, about 0.21 to about 0.28) that tends to absorb atleast a portion of impinging microwave energy and convert it to thermalenergy (i.e., heat) at the interface with the food item. Susceptors aretypically supported on a microwave energy transparent substrate, forexample, a polymer film, thereby collectively forming a “susceptorfilm”. Susceptor films, in turn, are often joined to a dimensionallystable supporting material (or “support”), for example, paper orpaperboard (“moisture-containing supports” or “fiber-based supports”),to collectively define a “supported susceptor film”.

Supported susceptor films may be used alone or in combination withnumerous other materials to form various microwave heating constructs.However, when the exposed side of the moisture-containing support isjoined to another layer using a continuous layer of adhesive, theresulting structure may tend to delaminate during heating. While notwishing to be bound by theory, it is believed that during heating, themoisture in the moisture-containing support is released as water vapor,which exerts a pressure on the adjacent layers of the structure. With nopath for the water vapor to escape, the layers of the structure tend todelaminate and loft away from one another. In some cases, this loftingor pillowing of the structure can cause the food item seated on thestructure to be turned over or toppled undesirably. This phenomenon hasbeen observed both when the supported susceptor film has been joined toanother fiber-based layer and when the supported susceptor film has beenjoined to another polymer film layer.

It is known that structures with more than one susceptor may generatemore heat than structures with a single susceptor. Thus, in suchmulti-susceptor structures, the risk of delamination may be amplified.For example, where a structure comprises a pair of susceptor filmsjoined to opposite sides of a support layer (e.g., paper or paperboard)using continuous layers of adhesive (as is needed to stabilize thesusceptor film), the structure may tend to delaminate or rupture uponheating. Thus, there remains a need for a multi-susceptor structure thatresists unintentional, uncontrolled delamination during use. There alsoremains a need for a method of making such a structure.

SUMMARY

This disclosure relates generally to various microwave energyinteractive structures, various constructs formed from such structures,various methods of making and such structures and constructs, andvarious methods of using such structures and constructs to heat, brown,and/or crisp a food item in a microwave oven.

The structures generally comprise a supported susceptor film, whichincludes a susceptor layer disposed between a polymer film layer and amoisture-containing support layer (e.g., paper or paperboard), and anadjoining layer, for example, a polymer film, paper layer, or paperboardlayer. The moisture-containing layer is joined to the adjoining layerusing any suitable method that allows for the release of moisture fromthe moisture-containing layer without causing uncontrolled orundesirable lamination of the structure.

In one example, the moisture-containing support layer is joined to theadjoining layer using a discontinuous layer of adhesive. Thediscontinuous layer of adhesive may be applied in a pattern, a randomconfiguration, or any other manner that results in the formation ofpassageways through the adhesive layer that allow the water vapor to bereleased from the structure.

By way of example, and not limitation, one exemplary structure accordingto the disclosure may include two supported susceptor films joined toone another using a discontinuous layer of adhesive. The supportedsusceptor films may be joined with their respective moisture-containinglayers facing one another, or with the moisture-containing layer of onesupported susceptor film being joined to the polymer film of the othersupported susceptor film.

Another exemplary structure according to the disclosure may include asupported susceptor film joined to a microwave energy interactiveinsulating material using a discontinuous layer of adhesive. Themicrowave energy interactive insulating material (“insulating material”)may be any suitable material that both alters the effect of microwaveenergy on an adjacent food item and that provides some degree of thermalinsulation from the microwave heating environment. For example, theinsulating material may include one or more susceptor layers incombination with one or more expandable insulating cells.

The various structures may be used to form numerous constructs,packages, or apparatuses (collectively “constructs”) for heating,browning, and/or crisping a food item in a microwave oven. Some of suchconstructs may include, but are not limited to, trays, platforms,sleeves, disks, cards, or pouches.

Other features, aspects, and embodiments of the invention will beapparent from the following description and accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

The description refers to the accompanying schematic drawings in whichlike reference characters refer to like parts throughout the severalviews, and in which:

FIG. 1A is a schematic cross-sectional view of an exemplary microwaveenergy interactive structure;

FIGS. 1B-1E schematically depict exemplary patterns of adhesive that maybe used to form the construct of FIG. 1A;

FIG. 2 is a schematic cross-sectional view of another exemplarymicrowave energy interactive structure;

FIG. 3 is a schematic cross-sectional view of still another exemplarymicrowave energy interactive structure;

FIG. 4A is a schematic cross-sectional view of yet another exemplarymicrowave energy interactive structure;

FIG. 4B is a schematic, partially cutaway, perspective view of a firstside of a construct for heating, browning, and/or crisping a food itemin a microwave oven, formed from the susceptor structure of FIG. 4A;

FIG. 4C is a schematic, partially cutaway, perspective view of a secondside of a construct for heating, browning, and/or crisping a food itemin a microwave oven, formed from the susceptor structure of FIG. 4A;

FIG. 4D is a schematic perspective view of a portion of the construct ofFIGS. 4B and 4C, after sufficient exposure to microwave energy;

FIG. 4E is a diagram of an exemplary process for forming the structureand construct of FIGS. 4A-4D;

FIGS. 5-7 are schematic cross-sectional views of exemplary microwaveenergy interactive insulating materials that may be used in theconstruct of FIGS. 4B and 4C;

FIG. 8A is a schematic top plan view of an exemplary microwave heatingconstruct including a plurality of microwave energy transparent areas;and

FIG. 8B is a schematic cross-sectional view of a portion of theconstruct of FIG. 8A.

DESCRIPTION

Various aspects of the invention may be understood further by referringto the figures. For purposes of simplicity, like numerals may be used todescribe like features. It will be understood that where a plurality ofsimilar features are depicted, not all of such features necessarily arelabeled on each figure. It also will be understood that the variouscomponents used to form the constructs may be interchanged. Thus, whileonly certain combinations are illustrated herein, numerous othercombinations and configurations are contemplated hereby.

FIG. 1A schematically illustrates a cross-sectional view of a portion ofsusceptor structure 100. The structure 100 includes a susceptor film102, namely, a layer of microwave energy interactive material 104 (e.g.,a first layer of microwave energy interactive material) supported on apolymer film 106. The susceptor film 102 is joined to a dimensionallystable, moisture-containing support layer 108 (e.g., a cellulose-basedsupport such as paper or paperboard) using a substantially continuouslayer of adhesive 110 to collectively define a supported susceptor film112. The supported susceptor film 112 is joined to an adjoining layer114 using a discontinuous layer of adhesive 116. Another layer ofmicrowave energy interactive material 118 (e.g., a second layer ofmicrowave energy interactive material) is disposed within the structure100 on a side of the adjoining layer 114 opposite the first layer ofmicrowave energy interactive material 104. The second layer of microwaveenergy interactive material 118 may be joined to the adjoining layer 114as shown, or in other embodiments, one or more layers may be disposedbetween the second layer of microwave energy interactive material 118and the adjoining layer 114. It is also contemplated that the structure100 may include other layers, as will be discussed further below.

The discontinuous layer of adhesive 116 generally defines joined areasand unjoined areas between the moisture-containing layer 108 and theadjoining layer 114. The unjoined areas may be at least partiallyinterconnected to define one or more passageways 120 that are in opencommunication with the exposed or open (e.g., unglued) peripheral edgesof the adjacent layers 108, 114 of the structure (not shown in FIG. 1A,see, e.g., FIGS. 4B and 4C). When the susceptor structure 100 is exposedto microwave energy, the layers of microwave energy interactive material104, 118 heat, thereby causing the moisture in the moisture-containinglayer 108 to be converted into water vapor. The water vapor may betransported through the open areas 120 within the adhesive layer 116(i.e., the areas not occupied by adhesive) to the exposed or ungluedperipheral edges of the structure 100, where the water vapor can bereleased. As a result, the various layers of the structure 100 are ableto remain laminated to one another. In contrast, the present inventorshave found that where a continuous layer of adhesive is used, the layerstend to delaminate from one another during use.

The discontinuous layer of adhesive 116 may comprise a pattern ofadhesive areas, a random (or seemingly random) arrangement of adhesiveareas, or any other suitable adhesive configuration. In someembodiments, the adhesive areas may comprise discrete adhesive areascircumscribed by non-adhesive areas, which define the ventingpassageways 120 in the structure 100. The adhesive areas may be solidshapes, open shapes that enclose or circumscribe non-adhesive areas(e.g., an annulus), or any combination thereof.

In one example, the adhesive areas of the discontinuous adhesive layer116 may be substantially circular in shape, such that the pattern ofadhesive resembles a plurality of dots, for example, as shown inschematic top plan view in FIG. 1B. The adhesive “dots” may have anysuitable size, spacing, and arrangement. The adhesive may generallycover less than about 80% of the surface of adjoining layer 114, and insome examples, the adhesive may cover less than about 75%, less thanabout 70%, less than about 65%, less than about 60%, less than about55%, less than about 50%, less than about 45%, less than about 40%, orless than about 35% of the adjoining layer 114. In some embodiments, theadhesive may cover from about 35% to about 80% of the adjoining layer114, for example, from about 45% to about 60% of the adjoining layer114, from about 34.9% to about 78.5% of the adjoining layer 114. It willbe appreciated that the degree of coverage for a particular heatingapplication may depend on numerous factors, including the level ofventing needed to prevent delamination of the structure. For example,where multiple susceptor layers (e.g., layers 104, 118) are used, moreventilation may be needed and the adhesive coverage area may be lessthan a similar structure including only one susceptor layer. Further,where the food item is to be seated on the susceptor structure, it hasbeen determined that less adhesive may be needed where the food item hassufficient weight to assist with keeping the various layers of thesusceptor structure intact.

In one exemplary embodiment, the adhesive dots may have a diameter ofabout 0.0625 in. (about 1.59 mm) and may be spaced about 0.0625 in.(about 1.59 mm) apart, such that the adhesive comprises about 78.5% ofthe total area of the structure. In another exemplary embodiment, theadhesive dots may have a diameter of about 0.125 in. (about 3.18 mm) andmay be spaced about 0.0625 in. (about 1.59 mm) apart, such that theadhesive comprises about 34.9% of the total area of the structure.However, countless other shapes, dimensions, and configurations may beused.

In another example, the adhesive areas of the discontinuous adhesivelayer 116 may comprise wavy lines, as shown in schematic top plan viewin FIG. 1C. In such an example, the spaces between the adhesive linesdefine the passageways for the water vapor to be released from thestructure. In still another example, the adhesive areas of thediscontinuous adhesive layer 116 may be substantially rectangular inshape, such that the pattern of adhesive resembles a plurality ofstaggered stripes, for example, as shown in schematic top plan view inFIG. 1D. In yet another example, the adhesive areas of the discontinuousadhesive layer 116 may be substantially cross-shaped, as shown inschematic top plan view in FIG. 1E. However, numerous other patterns maybe used, provided that such patterns allow the passage of moisturethrough the open areas 120 in the adhesive layer 116.

As stated previously, the adjoining layer 114 may be any material, forexample, a polymer film, paper, or paperboard. Further, it will beunderstood that additional layers may be joined to the adjoining layer114 if desired, as will be evident from the remaining discussion.

Numerous variations of the structure 100 of FIG. 1A are contemplated.For example, FIGS. 2-4A schematically depict some exemplary variationsof the microwave energy interactive structure 100 of FIG. 1A. Thevarious structures 200, 300, 400, 800 include features that are similarto structure 100 shown in FIG. 1A, except for variations noted andvariations that will be understood by those of skill in the art. Forsimplicity, the reference numerals of similar features are preceded inthe figures with a “2” (FIG. 2), “3” (FIG. 3), or “4” (FIG. 4A) insteadof a “1”.

In the exemplary structure 200 illustrated schematically in FIG. 2, theadjoining layer 214 may be a moisture-containing layer, for example,paper or paperboard. The second layer of microwave energy interactivematerial 218 may be joined to the adjoining layer 214 by a substantiallycontinuous layer of adhesive 222. The structure 200 may include a secondpolymer film 224 on a side of the second layer of microwave energyinteractive material 218 opposite the adhesive layer 222 to define asecond susceptor film 202′. The outermost surface of the first polymerfilm 206 or the second polymer film 224 may comprise a food-contactingsurface of the respective film layer.

Layers 214, 218, 222, 224 generally define a supported susceptor film212′ similar to supported susceptor film 212. The two supportedsusceptor films 212, 212′ are arranged with their respectivemoisture-containing layers 208, 214 facing one another on opposite sidesof the discontinuous layer of adhesive 216, such that the structure 200is generally symmetrical across the discontinuous layer of adhesive 216.In this example, it is contemplated that the water vapor from bothmoisture-containing layers 208, 214 may be transported from the interiorof the structure 200 via the discontinuities 220 in the adhesive layer216.

In another exemplary structure 300 illustrated schematically in FIG. 3,the adjoining layer 314 may be a polymer film. The structure 300includes a second moisture-containing layer 322 joined to the secondlayer of microwave energy interactive material 318 with a substantiallycontinuous layer of adhesive 324. The outermost surface of polymer film306 may comprise a food-contacting surface of the structure 300.

Layers 314, 318, 322, 324 generally define a supported susceptor film312′ similar to the supported susceptor film 312. In this embodiment,the two supported susceptor films 312, 312′ are in a “stacked”configuration and joined to one another by the discontinuous layer ofadhesive 316.

FIG. 4 schematically illustrates still another exemplary susceptorstructure 400. In this example, the structure 400 includes a supportedsusceptor film 412 joined to a microwave energy interactive insulatingmaterial 422 using a discontinuous layer of adhesive 416.

The supported susceptor film 412 comprises a susceptor layer 404supported on a polymer film layer 406 to define a susceptor film 402.The susceptor film 402 is joined to a moisture-containing layer 408(e.g., paperboard) with a substantially continuous layer of adhesive410.

The microwave energy interactive insulating material 422 includes asusceptor layer 418 supported on a first polymer film 424, collectivelyforming a susceptor film 402′. The susceptor film 402′ is joined to amoisture-containing substrate or support 426 (e.g., paper) using asubstantially continuous layer of adhesive 428, such that layers 418,424, 426, 428 define a supported susceptor film 412′ similar tosupported susceptor film 412. The microwave energy interactiveinsulating material 422 also includes an adjoining layer 414, in thisexample, a second polymer film 414 joined to the moisture-containingsupport 426 in a patterned configuration using an adhesive 430 or anyother suitable fastening material or technique. The pattern of adhesive430 generally defines a plurality of non-adhesive areas surrounded byadhesive areas, such that a plurality of closed cells 432 are formedbetween the support 426 and the second polymer film 414. The closedcells 432 are operative for inflating or expanding upon sufficientexposure to microwave energy, as will be discussed further below. In oneexample, the pattern of adhesive 430 may be a grid pattern, such thatthe closed cells 432 have a generally square shape. However, anysuitable pattern of adhesion and shape of closed cells 432 may be used.

The structures 100, 200, 300, 400 of FIGS. 1A, 2, 3, 4A and numerousothers encompassed by the present disclosure may be used to form variousmicrowave heating constructs, including, for example, cartons, trays,platforms, disks, sleeves, pouches, and so forth. By way of example, andnot limitation, FIGS. 4B and 4C schematically depict partial cutawayviews of opposed first and second sides of an exemplary microwave energyinteractive construct 434 formed (e.g., cut) from the susceptorstructure 400 of FIG. 4A. In this example, the construct 434 has agenerally circular shape, and therefore may be referred to as amicrowave energy interactive heating disk. The construct 434 may be usedfor heating, browning, and/or crisping a generally circular food item,for example, a pizza, in a microwave oven. However, numerous otherregular and irregular shapes are contemplated.

To use the construct 434, the food item F (e.g., a pizza) may be placedon a food-contacting surface 436 of the microwave energy interactiveinsulating material 422 (i.e., on the outermost surface of polymer film424, although it is contemplated that the construct 434 may be invertedand the outermost surface of polymer film 406 may comprise thefood-contacting surface in other embodiments) and placed in a microwaveoven. While not wishing to be bound by theory, it is believed that asthe susceptor 418 (shown schematically with stippling in FIG. 4B) heatsupon impingement by microwave energy, water vapor and other gasestypically held in the substrate 426, for example, paper, and any airtrapped in the closed cells 432 between the second polymer film 414 andthe substrate 426, expand, thereby causing the susceptor film 402′ andsubstrate 426 to loft or bulge away from the second polymer film 414, asschematically illustrated in FIG. 4D (which depicts only a portion ofthe microwave energy interactive heating disk 434). The resultinginsulating material 422 has a quilted or pillowed food-contacting sideor surface 436. In this inflated or expanded state, the susceptor 418 isurged towards the surface of the food item (e.g., the bottom surface ofthe food item F), to enhance browning and/or crisping, with the pillowedsurface of the insulating material 422 being able to conform moreclosely to the contours of the food item. For example, where the fooditem is a pizza, which tends to dome or crown during the freezingprocess, the expandable cells 432 of the insulating material 422 may bebrought into closer proximity with the domed area of the pizza, therebyproviding enhanced browning and/or crisping as compared with a flatsusceptor sheet. Further, the water vapor and other gases trapped in thecells 432 reduce the amount of heat transferred from the construct 434to the microwave heating environment, thereby further enhancing heating,browning, and/or crisping of the food item F. Additional features ofmicrowave energy interactive insulating materials are described indetail in U.S. Pat. No. 7,019,271, U.S. Pat. No. 7,351,942, and U.S.Pat. No. 7,923,669, each of which is incorporated by reference herein inits entirety. When microwave heating has ceased, the cells 432 typicallydeflate and return to a somewhat flattened state having a somewhatwrinkled appearance (not shown).

Likewise, upon sufficient exposure to microwave energy, susceptor 404(shown schematically with stippling in FIG. 4C) on the opposite side ofthe disk 434 converts at least a portion of the impinging microwaveenergy into thermal energy, which then can be transferred through thepaperboard layer 408 towards the lower surface of the food item F toenhance browning and/or crisping even further. Any water vapor generatedby the heating of the susceptor 404 can be released from the paperboard408 and transported through the passageways 420 in the discontinuousadhesive layer 416 (FIG. 4A) to the exposed edges 438 of the construct434.

Various methods of forming the construct 434 are contemplated. In oneexemplary method schematically illustrated in FIG. 4E, a paperboard basematerial 408 is unwound from a stock roll (not shown). An adhesive 410is applied to one side 440 of the paperboard 408 in a substantiallycontinuous configuration. A susceptor film 402 is then applied to thelayer of adhesive 410 with the metal layer 404 of the susceptor film 402facing the adhesive 410 to form the supported susceptor film 412, whichdefines the second side of the construct 434, shown in FIG. 4C.

In another operation that may or may not be integrated with theremainder of the process, paper 426 is unwound from a stock roll (notshown). A substantially continuous layer of adhesive 428 is applied to afirst side 442 of the paper 426. A susceptor film 402′ is then appliedto the layer of adhesive 428 with the metal layer 418 of the susceptorfilm 402′ facing the adhesive 428. An adhesive 430 is then applied tothe exposed side (i.e. the second side 444) of the paper 426 in agrid-like configuration. A polymer film 414 is then applied to theadhesive 430 to define a plurality of substantially closed cells 432between the paper 426 and the polymer film 414. This forms the microwaveenergy interactive insulating material 422 on the first side of theconstruct (FIG. 4B).

Returning to the supported susceptor film 412 previously formed, anadhesive 416 is applied in a patterned configuration (e.g., a dotpattern or other pattern, such as, but not limited to, the adhesivepatterns shown in FIGS. 1B-1E) to the exposed side 446 of the paperboard408. The microwave energy interactive insulating material 422 formedpreviously is then applied to the layer of adhesive 416 to join thepolymer film 414 to the paperboard 408. This forms the first side (i.e.,the food-contacting side) of the construct 434 (FIG. 4B).

The web is then sent to a die cutter, where the construct 434 is cutinto the desired shape, for example, a circle (e.g., FIGS. 4B and 4C),square, oval triangle, or any other desired shape.

It will be apparent that numerous other sequences of steps may be usedto form the construct 434. It also will be apparent that numerous othermicrowave energy interactive insulating materials or structures may beused to form a construct in accordance with the disclosure. Any of suchmaterials may be used alone or in combination, and in any configuration,to form the construct. Where multiple materials (or multiple layers ofthe same material) are used, the materials may be joined to one anotherpartially or completely, or may remain separate from one another (i.e.,unjoined).

For example, FIG. 5 schematically illustrates another exemplarymicrowave energy interactive insulating material 522 that may be usedinstead of the microwave energy interactive insulating material 422shown in FIGS. 4A-4D. In this example, the structure 522 includes apolymer film layer 502, a susceptor layer 504, an adhesive layer 506,and a paper layer 508. Additionally, the structure 500 includes a secondpolymer film layer 510, adhesive layer 512, and paper layer 514. Thelayers may be adhered or affixed by a patterned adhesive 516 thatdefines a plurality of substantially closed, expandable cells 518between the paper layers 508, 514.

Likewise, FIG. 6 schematically illustrates yet another exemplarymicrowave energy interactive insulating material 622 that may besuitable for use instead of the insulating material 422 shown in FIGS.4A-4D. In this example, the insulating material 622 includes a pair ofadjoined, symmetrical layer arrangements. If desired, the twosymmetrical arrangements may be formed by folding one layer arrangementonto itself.

The first symmetrical layer arrangement, beginning at the top of thedrawing, comprises a polymer film layer 602, a susceptor layer 604, anadhesive layer 606, and a paper or paperboard layer 608. The adhesivelayer 606 joins the polymer film 602 and the susceptor layer 604 to thepaperboard layer 608. The second symmetrical layer arrangement,beginning at the bottom of the drawing, also comprises a polymer filmlayer 610, a susceptor layer 612, an adhesive layer 614, and a paper orpaperboard layer 616. A patterned adhesive layer 618 is provided betweenthe two paper layers 608, 616 to define a plurality of closed cells 620that are adapted to inflate when sufficiently exposed to microwaveenergy. While not wishing to be bound by theory, it is believed that theadditional susceptor layer results in greater heating and expansion ofthe insulating cells, thereby providing more thermal insulation ascompared with an insulating material having a single susceptor layer.

It will be recognized that each of the exemplary insulating materialspreviously described include a moisture-containing layer (e.g. paper)that is believed to release at least a portion of the vapor thatinflates the expandable cells. However, it is contemplated thatinsulating structures without such moisture-containing layers also maybe used instead of the insulating material 422 shown in FIGS. 4A-4D toform the construct 434 (or any other construct).

For example, FIG. 7 illustrates one example of an expandable cellinsulating material 722 that inflates without the need for amoisture-containing layer, for example, paper. In this example, one ormore reagents are used to generate a gas that inflates the cells.

A thin layer of microwave interactive material 702 is supported on afirst polymer film 704 to form a susceptor film 706. One or morereagents 708, optionally within a coating, lie adjacent at least aportion of the layer of microwave interactive material 702. The reagent708 coated susceptor film 706 is joined to a second polymer film 710using a patterned adhesive 712 or other material, or using thermalbonding, ultrasonic bonding, or any other suitable technique, such thatclosed cells 714 (shown as a void) are formed in the material 700.

Numerous reagents may be suitable for use in the structure 722. Forexample, the reagents may comprise sodium bicarbonate (NaHCO₃) and asuitable acid. When exposed to heat, the reagents react to producecarbon dioxide. As another example, the reagent may comprise a blowingagent. Examples of blowing agents that may be suitable include, but arenot limited to, p-p′-oxybis(benzenesulphonylhydrazide),azodicarbonamide, and p-toluenesulfonylsemicarbazide. However, it willbe understood that numerous other reagents and released gases arecontemplated hereby.

As the microwave energy interactive material 702 heats upon impingementby microwave energy, water vapor or other gases are released from (orgenerated by) the reagent 708, thereby exerting pressure on thesusceptor film 706 on one side and the second polymer film 710 on theother side of the closed cells 714, as discussed in connection with thevarious other insulating materials described above. Even without a paperor paperboard layer, the gas resulting from the reagent is sufficientboth to inflate the expandable cells and to absorb any excess heat fromthe susceptor. Such materials are described further in U.S. Pat. No.7,868,274, which is incorporated by reference herein in its entirety.

Countless other microwave energy interactive structures and constructsare contemplated by the disclosure. If desired, any of such structuresmay include one or more areas that are transparent to microwave energy.Such microwave energy transparent areas transmit microwave energy and,in some instances, may cause the formation of localized electric fieldsthat enhance heating, browning, and/or crisping of an adjacent fooditem. The transparent areas may be sized, positioned, and/or arranged tocustomize the heating, browning, and/or crisping of a particular area ofthe food item to be heated.

For example, FIG. 8A schematically illustrates a top plan view ofanother microwave heating construct 800 (e.g., a microwave heating disk)that generally includes a susceptor 802 (shown schematically withstippling) that circumscribes a plurality of microwave energytransparent areas 804, 806 (shown schematically in white). In thisexample, the disk 800 has a substantially circular shape. However, anyregular or irregular shape may be used.

The disk 800 includes a central region 808 and a peripheral region 810.In the central region 808 of the disk 800, the microwave energytransparent areas 804 are substantially circular in shape, with theconcentration of microwave energy transparent areas 804 decreasing fromthe center of the disk 800 outwardly towards the peripheral region 810.However, other configurations are contemplated. For example, anotherexemplary arrangement of microwave energy transparent areas is disclosedin U.S. Pat. Nos. 6,414,290 and 6,765,182, which are incorporated byreference herein in their entirety.

In the peripheral region 810, the microwave energy transparent areas 806are substantially square in shape and arranged in rows and columns, suchthat the microwave energy interactive material in the peripheral region810 has a grid-like appearance. As stated above, the percent transparentarea may be varied as needed to achieve the desired heating, browning,and/or crisping of the food item. Such areas may be formed in anysuitable manner, as will be described below.

FIG. 8B schematically illustrates a cross-sectional view of a portion ofthe microwave heating disk 800 of FIG. 8A. The microwave heating disk800 includes a pair of microwave energy interactive elements 802 a, 802b, for example, susceptors (or susceptor layers), supported onrespective microwave energy transparent substrates 812 a, 812 b, forexample, polymer film layers, to collectively define respectivesusceptor films or susceptor film layers 814 a, 814 b. Susceptor 802 acircumscribes at least one, and in some examples, a plurality, ofmicrowave energy transparent (i.e., inactive) areas 804 (or 806, FIG.8A).

Each susceptor is joined respectively to a respective microwave energytransparent, dimensionally stable support or support layer 816 a, 816 b,for example, paper, using a respective substantially continuous adhesivelayer 818 a, 818 b to define respective supported susceptor films 820 a,820 b. The supported susceptor films 820 a, 820 b may be joined to oneanother using a discontinuous layer of adhesive 822 (e.g., a dot patternor other pattern, such as, but not limited to, the adhesive patternsshown in FIGS. 1B-1E). In turn, support layer 816 b is joined to adouble faced corrugated material 824, which includes a plurality offlutes or corrugations 826 between facing layers 828 a, 828 b.

In the illustrated embodiment, the support layer 816 b is joined to thefacing layer 828 a using a discontinuous layer of adhesive 830. However,in some embodiments, the layer of adhesive 830 may be substantiallycontinuous. While not wishing to be bound by theory, it is believed thatsome facing layers 828 a are somewhat textured and/or porous, which mayallow water vapor to be vented from the support layer 816 b withoutcausing delamination of the layers 816 b, 828 a.

In another embodiment (not shown), the support layer 816 b anddiscontinuous adhesive layer 830 may be omitted, such that the susceptorfilm 814 b is joined directly to the facing layer 828 a. In such a case,the layer of adhesive 818 b joining the susceptor film 814 b to thefacing layer 828 a may be substantially continuous (as shown).

Numerous other microwave heating constructs are encompassed by thedisclosure. Any of such structures or constructs may be formed fromvarious materials, provided that the materials are substantiallyresistant to softening, scorching, combusting, or degrading at typicalmicrowave oven heating temperatures, for example, at from about 250° F.to about 425° F. The materials may include microwave energy interactivematerials, for example, those used to form susceptors and othermicrowave energy interactive elements, and microwave energy transparentor inactive materials, for example, those used to form the remainder ofthe construct.

The microwave energy interactive material may be an electroconductive orsemiconductive material, for example, a metal or a metal alloy providedas a metal foil; a vacuum deposited metal or metal alloy; or a metallicink, an organic ink, an inorganic ink, a metallic paste, an organicpaste, an inorganic paste, or any combination thereof. Examples ofmetals and metal alloys that may be suitable include, but are notlimited to, aluminum, chromium, copper, inconel alloys(nickel-chromium-molybdenum alloy with niobium), iron, magnesium,nickel, stainless steel, tin, titanium, tungsten, and any combination oralloy thereof.

Alternatively, the microwave energy interactive material may comprise ametal oxide, for example, oxides of aluminum, iron, and tin, optionallyused in conjunction with an electrically conductive material. Anothermetal oxide that may be suitable is indium tin oxide (ITO). ITO has amore uniform crystal structure and, therefore, is clear at most coatingthicknesses.

Alternatively still, the microwave energy interactive material maycomprise a suitable electroconductive, semiconductive, or non-conductiveartificial dielectric or ferroelectric. Artificial dielectrics compriseconductive, subdivided material in a polymeric or other suitable matrixor binder, and may include flakes of an electroconductive metal, forexample, aluminum.

While susceptors are illustrated herein, the construct also may includea foil or high optical density evaporated material having a thicknesssufficient to reflect a substantial portion of impinging microwaveenergy. Such elements are typically formed from a conductive, reflectivemetal or metal alloy, for example, aluminum, copper, or stainless steel,in the form of a solid “patch” generally having a thickness of fromabout 0.000285 inches to about 0.05 inches, for example, from about0.0003 inches to about 0.03 inches. Other such elements may have athickness of from about 0.00035 inches to about 0.020 inches, forexample, 0.016 inches.

Larger microwave energy reflecting elements may be used where the fooditem is prone to scorching or drying out during heating and therefore,may be referred to as shielding elements. Smaller microwave energyreflecting elements may be used to diffuse or lessen the intensity ofmicrowave energy. A plurality of smaller microwave energy reflectingelements also may be arranged to form a microwave energy directingelement to direct microwave energy to specific areas of the food item.If desired, the loops may be of a length that causes microwave energy toresonate, thereby enhancing the distribution effect. Microwave energydistributing elements are described in U.S. Pat. Nos. 6,204,492,6,433,322, 6,552,315, and 6,677,563, each of which is incorporated byreference in its entirety.

If desired, any of the numerous microwave energy interactive elementsdescribed herein or contemplated hereby may be substantially continuous,that is, without substantial breaks or interruptions, or may bediscontinuous, for example, by including one or more breaks or aperturesthat transmit microwave energy therethrough. The breaks or apertures maybe sized and positioned to heat particular areas of the food itemselectively. The breaks or apertures may extend through the entirestructure, or only through one or more layers. The number, shape, size,and positioning of such breaks or apertures may vary for a particularapplication depending on the type of construct being formed, the fooditem to be heated therein or thereon, the desired degree of shielding,browning, and/or crisping, whether direct exposure to microwave energyis needed or desired to attain uniform heating of the food item, theneed for regulating the change in temperature of the food item throughdirect heating, and whether and to what extent there is a need forventing.

It will be understood that the aperture may be a physical aperture orvoid in one or more layers or materials used to form the construct, ormay be a non-physical “aperture” (not shown). A non-physical aperture isa microwave energy transparent area (e.g., microwave energy transparentareas 804, 806) that allows microwave energy to pass through thestructure without an actual void or hole cut through the structure. Suchareas may be formed by simply not applying microwave energy interactivematerial to the particular area, or by removing microwave energyinteractive material in the particular area, or by mechanicallydeactivating the particular area (rendering the area electricallydiscontinuous). Alternatively, the areas may be formed by chemicallydeactivating the microwave energy interactive material in the particulararea, thereby transforming the microwave energy interactive material inthe area into a substance that is transparent to microwave energy (i.e.,microwave energy inactive). While both physical and non-physicalapertures allow the food item to be heated directly by the microwaveenergy, a physical aperture also provides a venting function to allowsteam or other vapors to escape from the interior of the construct.

The arrangement of microwave energy interactive and microwave energytransparent areas may be selected to provide various levels of heating,as needed or desired for a particular application. For example, wheregreater heating is desired, the total inactive (i.e., microwave energytransparent) area may be increased. In doing so, more microwave energyis transmitted to the food item. Alternatively, by decreasing the totalinactive area, more microwave energy is absorbed by the microwave energyinteractive areas, converted into thermal energy, and transmitted to thesurface of the food item to enhance heating, browning, and/or crisping.

In some instances, it may be beneficial to create one or morediscontinuities or inactive regions to prevent overheating or charringof the construct. Such areas may be formed by forming these areas of theconstruct without a microwave energy interactive material, by removingany microwave energy interactive material that has been applied, or bydeactivating the microwave energy interactive material in these areas,as discussed above.

Further still, one or more panels, portions of panels, or portions ofthe construct may be designed to be microwave energy inactive to ensurethat the microwave energy is focused efficiently on the areas to beheated, browned, and/or crisped, rather than being lost to portions ofthe food item not intended to be browned and/or crisped or to theheating environment. This may be achieved using any suitable technique,such as those described above.

As stated above, the microwave energy interactive material (e.g.,susceptors 104, 118, 204, 218, 304, 318, 404, 418, 504, 604, 612, 702,802 a, 802 b) may be supported on a microwave inactive or transparentsubstrate (e.g., polymer films 106, 206, 224, 306, 314, 406, 424, 502,602, 610, 704, 812 a, 812 b) for ease of handling and/or to preventcontact between the microwave energy interactive material and the fooditem. The outermost surface of the polymer film may define at least aportion of the food-contacting surface of the package (e.g., surface 436of polymer film 424). Examples of polymer films that may be suitableinclude, but are not limited to, polyolefins, polyesters, polyamides,polyimides, polysulfones, polyether ketones, cellophanes, or anycombination thereof. In one particular example, the polymer filmcomprises polyethylene terephthalate. The thickness of the filmgenerally may be from about 35 gauge to about 10 mil. In each of variousexamples, the thickness of the film may be from about 40 to about 80gauge, from about 45 to about 50 gauge, about 48 gauge, or any othersuitable thickness. Other non-conducting substrate materials such aspaper and paper laminates, metal oxides, silicates, cellulosics, or anycombination thereof, also may be used.

The microwave energy interactive material may be applied to thesubstrate in any suitable manner, and in some instances, the microwaveenergy interactive material is printed on, extruded onto, sputteredonto, evaporated on, or laminated to the substrate. The microwave energyinteractive material may be applied to the substrate in any pattern, andusing any technique, to achieve the desired heating effect of the fooditem. For example, the microwave energy interactive material may beprovided as a continuous or discontinuous layer or coating includingcircles, loops, hexagons, islands, squares, rectangles, octagons, and soforth.

Numerous materials may serve as a moisture-containing layer (e.g.,moisture-containing layers 108, 208, 214, 308, 408, 816 a) in thevarious structures and constructs. In one example, themoisture-containing layer comprises paper having basis weight of fromabout 15 to about 60 lbs/ream (lb/3000 sq. ft.), for example, from about20 to about 40 lbs/ream. In another example, the paper has a basisweight of about 25 lbs/ream. In another example, the moisture-containinglayer comprises paperboard having a basis weight of from about 60 toabout 330 lbs/ream, for example, from about 80 to about 140 lbs/ream.The paperboard generally may have a thickness of from about 6 to about30 mils, for example, from about 12 to about 28 mils. In one particularexample, the paperboard has a thickness of about 12 mils. Any suitablepaperboard may be used, for example, a solid bleached or solidunbleached sulfate board, such as SUS® board, commercially availablefrom Graphic Packaging International.

The package may be formed according to numerous processes known to thosein the art, including using adhesive bonding, thermal bonding,ultrasonic bonding, mechanical stitching, or any other suitable process.Any of the various components used to form the package may be providedas a sheet of material, a roll of material, or a die cut material in theshape of the package to be formed (e.g., a blank).

It will be understood that with some combinations of elements andmaterials, the microwave energy interactive element may have a grey orsilver color that is visually distinguishable from the substrate or thesupport. However, in some instances, it may be desirable to provide apackage having a uniform color and/or appearance. Such a package may bemore aesthetically pleasing to a consumer, particularly when theconsumer is accustomed to packages or containers having certain visualattributes, for example, a solid color, a particular pattern, and so on.Thus, for example, the present disclosure contemplates using a silver orgrey toned adhesive to join the microwave energy interactive element tothe support, using a silver or grey toned support to mask the presenceof the silver or grey toned microwave energy interactive element, usinga dark toned substrate, for example, a black toned substrate, to concealthe presence of the silver or grey toned microwave energy interactiveelement, overprinting the metallized side of the polymer film with asilver or grey toned ink to obscure the color variation, printing thenon-metallized side of the polymer film with a silver or grey ink orother concealing color in a suitable pattern or as a solid color layerto mask or conceal the presence of the microwave energy interactiveelement, or any other suitable technique or combination of techniques.

The disclosure may be understood further from the following example,which is not intended to be limiting in any manner.

EXAMPLE 1

Two supported susceptor films were joined to one another with theirrespective paper support layers facing one another using a continuouslayer of adhesive. The resulting structure was heated without a load(i.e., without a food item) in a microwave oven for about 20 seconds.The layers of the structure began to delaminate and loft away from oneanother.

The supported susceptor films then were joined to one another with theirrespective paper support layers facing one another using a patternedadhesive. In particular, the patterned adhesive consisted of a dotpattern, where the dots had a diameter of about 0.125 in. and a spacingof about 0.0625 in. The resulting structure was heated without a load(i.e., without a food item) in a microwave oven for about 20 seconds.The layers of the structure remained intact.

EXAMPLE 2

A first supported susceptor film comprising a metalized polyethyleneterephthalate film joined to paperboard was pressed into a trayincluding a pair of elevated platforms. Such trays are described in U.S.Patent Application Publication Nos. US 2008/0164178 A1, published Jul.10, 2008, and US 2008/0000896 A1, published Jan. 3, 2008, which areincorporated by reference herein in their entirety. The tray was used toheat a 10″ Tombstone pizza in a microwave oven for about 5 minutes. Thebottom crust of the pizza was browned and or crisped acceptably.

A second tray was formed by joining a second supported susceptor film tothe first supported susceptor film. The second supported susceptor filmincluded a metalized polyethylene terephthalate film joined to paper.The first and second supported susceptor films were joined to oneanother with the paperboard and paper layer facing one another using thedot adhesive pattern described in Example 1. The tray was used to heat a10″ Tombstone pizza in a microwave oven for about 5 minutes. The bottomcrust of the pizza was browned and or crisped exceptionally. Thus,although the single susceptor tray produced suitable results, the dualsusceptor structure achieved superior browning and crisping of the pizzacrust.

While the present invention is described herein in detail in relation tospecific aspects and embodiments, it is to be understood that thisdetailed description is only illustrative and exemplary of the presentinvention and is made merely for purposes of providing a full andenabling disclosure of the present invention and to set forth the bestmode of practicing the invention known to the inventors at the time theinvention was made. The detailed description set forth herein isillustrative only and is not intended, nor is to be construed, to limitthe present invention or otherwise to exclude any such otherembodiments, adaptations, variations, modifications, and equivalentarrangements of the present invention. All directional references (e.g.,upper, lower, upward, downward, left, right, leftward, rightward, top,bottom, above, below, vertical, horizontal, clockwise, andcounterclockwise) are used only for identification purposes to aid thereader's understanding of the various embodiments of the presentinvention, and do not create limitations, particularly as to theposition, orientation, or use of the invention unless specifically setforth in the claims. Joinder references (e.g., joined, attached,coupled, connected, and the like) are to be construed broadly and mayinclude intermediate members between a connection of elements andrelative movement between elements. As such, joinder references do notnecessarily imply that two elements are connected directly and in fixedrelation to each other. Further, various elements discussed withreference to the various embodiments may be interchanged to createentirely new embodiments coming within the scope of the presentinvention.

What is claimed is:
 1. A microwave energy interactive structurecomprising: at least one peripheral edge; a first susceptor filmcomprising a first layer of microwave energy interactive materialsupported on a first polymer film; a moisture-containing layer joined tothe first layer of microwave energy interactive material; an adjoininglayer joined to the moisture-containing layer such that themoisture-containing layer is disposed between the susceptor film and theadjoining layer, the adjoining layer being joined to themoisture-containing layer by a discontinuous adhesive layer, wherein thediscontinuous adhesive layer comprises a plurality of joined areasspaced apart from one another by unjoined areas, the unjoined areasbeing at least partially interconnected to define at least onepassageway that is in open communication with the at least oneperipheral edge for allowing water vapor to be transported through theat least one passageway and to be released at the at least oneperipheral edge, the at least one passageway being generally parallel tothe moisture-containing layer; and a second layer of microwave energyinteractive material on a side of the adjoining layer opposite themoisture-containing layer.
 2. The structure of claim 1, wherein theadjoining layer comprises a second polymer film.
 3. The structure ofclaim 2, wherein the moisture-containing layer is a firstmoisture-containing layer, and the structure further comprises a secondmoisture-containing layer on a side of the second layer of microwaveenergy interactive material opposite the second polymer film.
 4. Thestructure of claim 3, wherein the second moisture-containing layer isjoined to the second layer of microwave energy interactive material by asubstantially continuous layer of adhesive.
 5. The structure of claim 3,further comprising a corrugated material joined to the secondmoisture-containing layer on a side of the moisture-containing layeropposite the second layer of microwave energy interactive material. 6.The structure of claim 5, wherein the corrugated material is a doublefaced corrugated material.
 7. The structure of claim 5, wherein thecorrugated material is joined to the second moisture-containing layer bya discontinuous adhesive layer, wherein the discontinuous adhesive layercomprises a plurality of joined areas, each joined area beingcircumscribed by an unjoined area.
 8. The structure of claim 5, whereinthe first layer of microwave energy interactive material circumscribes aplurality of microwave energy transparent areas.
 9. The structure ofclaim 8, wherein the plurality of microwave energy transparent areasincludes a first plurality of microwave energy transparent areasdefining a peripheral region of the structure and a plurality of secondmicrowave energy transparent areas defining a central area of thestructure.
 10. The structure of claim 9, wherein each microwave energytransparent area of the first plurality of microwave energy transparentareas is substantially square in shape, such that the microwave energyinteractive material has a substantially grid shape.
 11. The structureof claim 9, wherein each microwave energy transparent area of the secondplurality of microwave energy transparent areas is substantiallycircular in shape.
 12. The structure of claim 9, wherein the structurecomprises a microwave heating disk.
 13. The structure of claim 12,wherein the first polymer film is for contacting a food item.
 14. Thestructure of claim 1, wherein the adjoining layer is amoisture-containing layer.
 15. The structure of claim 14, wherein theadjoining layer comprises paper or paperboard.
 16. The structure ofclaim 15, wherein the second layer of microwave energy interactivematerial is joined to the adjoining layer by a substantially continuouslayer of adhesive.
 17. The structure of claim 16, wherein the polymerfilm is a first polymer film, and the structure further comprises asecond polymer film on a side of the second layer of microwave energyinteractive material opposite the adjoining layer.
 18. The structure ofclaim 1, wherein the adjoining layer comprises a second polymer film,the moisture-containing layer is a first moisture-containing layer, andthe structure further comprises a second moisture-containing layerdisposed between the second polymer film and the second layer ofmicrowave energy interactive material, the second moisture-containinglayer being joined to the second polymer film by a patterned adhesivethat defines a plurality of closed cells between the second-moisturecontaining layer and the polymer film, each closed cell comprising anunjoined area, and a third polymer film on a side of the second layer ofmicrowave energy interactive material opposite the secondmoisture-containing layer.
 19. The structure of claim 18, wherein theclosed cells are for inflating in response to sufficient exposure tomicrowave energy.
 20. The structure of claim 18, wherein the thirdpolymer film is for contacting a food item.
 21. The structure of claim18, wherein the first polymer film is for contacting a food item. 22.The structure of claim 1, wherein the adhesive of the discontinuousadhesive layer covers less than about 80% of the adjoining layer. 23.The structure of claim 1, wherein the adhesive of the discontinuousadhesive layer covers about 35% of the adjoining layer.
 24. Thestructure of claim 1, wherein the moisture-containing layer comprisespaper or paperboard.
 25. The structure of claim 1, wherein themoisture-containing layer is joined to the first layer of microwaveenergy interactive material by a substantially continuous layer ofadhesive.
 26. The structure of claim 1, wherein at least one joined areaof the plurality of joined areas of the discontinuous adhesive layer iscircumscribed by the unjoined areas.
 27. The structure of claim 1,wherein the at least one peripheral edge comprises respective edges ofthe moisture-containing layer and the adjoining layer, the at least onepassageway being at least partially defined by at least a portion of therespective edges of the moisture-containing layer and the adjoininglayer at the peripheral edge.
 28. The structure of claim 1, wherein theadjoining layer is substantially continuous.
 29. The structure of claim1, wherein the first layer of microwave energy interactive material issubstantially continuous.